| Scenario | Input | Source | Photoperiod | Adjustments | Effective PPFD | DLI |
|---|---|---|---|---|---|---|
| Leafy greens shelf | 12,000 lux | Cool white LED | 16 h | Loss 10% | ~166 µmol/m²/s | ~9.6 mol/m²/day |
| Seedlings with shade | 8,000 lux | Fluorescent | 18 h | Shade 30% | ~76 µmol/m²/s | ~4.9 mol/m²/day |
| Herb corner | 250 fc | Warm white LED | 14 h | Loss 15% | ~76 µmol/m²/s | ~3.8 mol/m²/day |
| Fruiting tent | 450 µmol/m²/s | LED preset | 12 h | Uniform 85% | ~450 µmol/m²/s | ~19.4 mol/m²/day |
| Greenhouse estimate | 300 W/m² | Sunlight | 10 h | Glazing 75% | ~389 µmol/m²/s | ~14.0 mol/m²/day |
- lux = foot-candles × 10.7639
- lux = PPFD × (lux per PPFD)
- PPFD = lux ÷ (lux per PPFD)
- lux = (W/m²) × (lm/W) (uses a luminous-efficacy estimate)
- Adjusted = Raw × glazing × (1−shade) × (1−loss)
- DLI = PPFD × photoperiod_seconds ÷ 1,000,000
- Lumens = lux × area and PPF ≈ PPFD × area
- Minimum estimate = Average × uniformity
- Measure your canopy with a light meter, or use a fixture spec.
- Select the unit you have: lux, foot-candles, PPFD, or W/m².
- Pick a light-source preset, then refine the conversion factors.
- Enter canopy area and photoperiod to estimate totals and DLI.
- Apply glazing, shade, and loss percentages to match real conditions.
- Choose a plant profile, or set custom PPFD and DLI targets.
- Press Calculate and review the summary and suggestions above.
- Download CSV or PDF to keep a record for planning.
1) Lux and foot-candles for quick field checks
Lux and foot-candles describe how bright light appears to human eyes. Gardeners often start here because inexpensive meters report lux, and many fixture sheets list foot-candles. However, these units are weighted toward green wavelengths, so two lights with equal lux can deliver different plant-usable photons. Use lux as a fast screening tool, then rely on PPFD and DLI for planning growth targets.
2) PPFD estimates the photosynthetic photon stream
PPFD (µmol/m²/s) approximates how many photosynthetic photons reach a square meter each second. This calculator converts lux to PPFD using a selectable “lux per PPFD” factor. Adjust it when you know your spectrum or have manufacturer data. Cooler white sources often produce higher lux per PPFD than sunlight, while specialized horticulture spectra can shift the factor noticeably.
3) DLI links intensity and time into daily totals
DLI (mol/m²/day) is the daily sum of PPFD over the photoperiod. It is often the best single number for comparing schedules. If your intensity is limited, a longer photoperiod can raise DLI without changing fixtures, provided your plants tolerate longer days. This tool shows both average and minimum estimates using a uniformity percentage.
4) Real-world losses: glazing, shade, and layout
Greenhouse glazing, shade cloth, distance, reflector spill, and dirty lenses reduce usable light. The calculator applies these as multiplicative reductions so you can quickly test improvements. For example, moving from 30% shade to 10% shade increases effective PPFD by about 29% at the canopy, assuming other factors stay constant.
5) Example data you can replicate
Try this repeatable check: input 12,000 lux, select Cool white LED, set 16 h photoperiod, and keep losses at 10%. You should see roughly 166 µmol/m²/s and about 9.6 mol/m²/day. Then increase losses to 25% to observe how DLI drops and why cleaning and layout matter.
1) Why does lux-to-PPFD vary by light source?
Lux is weighted for human vision, not plant response. Different spectra produce different lux readings for the same photon output. The “lux per PPFD” factor approximates that spectral effect.
2) Should I trust W/m² input for grow planning?
Use it cautiously. W/m² describes radiant power, not plant photons. The tool converts it to lux using an lm/W estimate, so accuracy depends on your efficacy assumption.
3) What is a good uniformity percentage?
For small shelves, 85–95% is attainable with good spacing and diffusion. If uniformity is lower, some plants will receive much less PPFD than the average.
4) Can I increase DLI without buying new lights?
Often, yes. Extending photoperiod increases DLI if intensity stays stable. Also reduce shade, clean covers, and improve reflection to recover lost light.
5) Which target should I prioritize, PPFD or DLI?
DLI is usually better for scheduling because it captures time. PPFD matters for plant form and stress; very high PPFD can require CO₂ and careful temperature control.
6) Why are my measured lux values inconsistent?
Readings vary with sensor angle, distance, shadows, and hotspot patterns. Take multiple readings across the canopy, keep the sensor level, and average the values.
7) Does this replace a quantum sensor?
No. It provides informed estimates and planning support. A calibrated quantum sensor gives the most accurate PPFD and DLI, especially for unusual spectra.